Off the AA website:
The European regulations governing the sale and after-sales servicing of new cars changed in October 2003. For new cars purchased after that date you are no longer obliged during the warranty period to get the car serviced by a franchise dealer.
You must however continue to get the car serviced according to the manufacturer's recommended schedule and criteria using only manufacturer approved parts.
The legislation only applies to the part of the warranty offered by the manufacturer, i.e. insurance-backed extended warranties offered by dealers are not covered.
If you do have the car serviced outside the dealer network it is essential that it's done to the maker's recommended schedule and criteria using approved parts. You must also keep records to enable you to demonstrate to the manufacturer that servicing was undertaken to their requirements.
Warranty work should still be undertaken by the franchised dealer as it is easier for them to deal directly with the manufacturer.
There's more information in the consumer advice section of the Society of Motor Manufacturers and Traders (SMMT) website,
www.smmt.co.uk.